The present invention is related to an apparatus for feeding a fluid of elevated pressure into a steam generator, and particularly to a fluid feeding apparatus capable of gradually and circulatorily elevating the head of a fluid. By and large, to supply liquid into a pressure vessel, it is necessary to raise the head of the liquid to an amount higher than the internal pressure of the vessel by a pump of high output, such as a multi-stage turbine pump. However, the utilization of such a pump has disadvantages in that, unless one allows for high electricity consumption, it is rather difficult to maintain a plurality of impellers which are connected in tandem, in balance.
If the factory intends to recover condensates of various pressures and temperatures from different sources and feed them into a steam boiler for the sake of saving energy, one would encounter great difficulty, such as back pressure resulting in the exhaust port of a steam trap. In oder to maintain the temperature as the highest possible level and to eliminate the loss of the flash stream, generally a closed recovery system is adopted. In the closed recovery system, the condensates of different pressures from different steam traps are directed into a reservoir which is kept at the lowest pressure by releasing the excess pressure through a pressure control valve to prevent it from causing back pressure. As a consequence, a high-output pump of a centrifugal type is necessary for feeding the condensate into a steam boiler. Taking the net positive suction head into consideration, the pressure on the impeller will oftentimes be greatly reduced, which will result in the phenomenon of flash steam. The phenomenon of the flash steam brings the pump into idle motion so as to cause cavation and water hammer and can cause damage to the pump. To eliminate the phenomenon of flash steam, an additional means for elevating the pressure should be provided for streamlining the operation. However, in view of the fact that in a closed heat recovery system, when the temperature of the recovered condensate reaches 120 degrees Centigrade, about 1 kg/cm.sup.2 G of back pressure at the exhaust port of the steam trap is created, whereas when the temperature is raised to up to 145 degrees Centigrade, up to 3 kg/cm.sup.2 G of back pressure will result. In order to avoid confronting this problem, some factories would rather continue to utilize the open recovery system and discharge a great deal of heat energy into the atmosphere.
In Taiwan Utility Model Pat. No. 23879 issued to this inventor, a closed recovery system is disclosed as schematically shown in FIG. 1, In the prior invention, the condensates of various pressures are divided into a first condensate of a pressure higher than a pressure of a second condensate which acts as an actuating fluid for the second condensate in an injector. Subsequently a third condensate of the highest pressure acts as an actuating fluid for the mixture of the first and second condensates, and etc. After a series of operations of injectors, the pressure of the recovered condensates will gradually increase without the drawback of the accompanying problem of back pressure. The pressure of the intermixed condensate through the last operation of the injector can be elevated as an actuating fluid so that the pressure of the intermixed condensate can be further elevated to a desired value. However, a system for implementing the above process is rather bulky, and further improvement over the prior system is still attempted.